Flip-Flop Study Material
Flip-flops are essential components in sequential logic circuits. They are used for data storage,
synchronization, and state machines in digital electronics. Below is a detailed study guide on flip-
flops, covering their types, working principles, truth tables, and applications.
1. Basics of Flip-Flops
A flip-flop is a bistable multivibrator, meaning it has two stable states (0 or 1) and can store one bit
of data. Flip-flops are edge-triggered (operate on clock pulses), unlike latches, which are level-
triggered.
1.1 Types of Flip-Flops
• SR Flip-Flop (Set-Reset)
• D Flip-Flop (Data/Delay)
• JK Flip-Flop
• T Flip-Flop (Toggle)
Each flip-flop type has different behaviors and use cases.
2. Types of Flip-Flops & Working
2.1 SR Flip-Flop (Set-Reset Flip-Flop)
Function: Stores a single bit based on Set (S) and Reset (R) inputs.
• Logic Circuit: Uses two NOR gates (or two NAND gates for active-low input).
• Truth Table:
S R Q (Next State) Q' (Complement)
0 0 No Change No Change
0 1 0 (Reset) 1
1 0 1 (Set) 0
1 1 Invalid State Invalid
• Problem: The S = 1, R = 1 condition leads to an undefined state (not allowed).
• Solution: Use a JK Flip-Flop instead.
2.2 D Flip-Flop (Data/Delay Flip-Flop)
Function: Stores input D on the clock edge (prevents invalid states like SR Flip-Flop).
• Logic Circuit: Created by adding a NOT gate to an SR Flip-Flop.
• Truth Table:
D Clock Q (Next State)
0↑ 0
1↑ 1
• Feature: The D input directly determines the output Q, making it useful for registers &
memory units.
• Application: Used in shift registers, latches, memory storage.
2.3 JK Flip-Flop
Function: Eliminates the invalid state problem of the SR Flip-Flop.
• Logic Circuit: Uses two AND gates with feedback loops.
• Truth Table:
J K Q (Next State)
0 0 No Change
0 1 0 (Reset)
1 0 1 (Set)
1 1 Toggle (Q → Q')
• Feature: When J = 1, K = 1, the output toggles (flips between 0 and 1).
• Application: Used in counters, frequency dividers.
2.4 T Flip-Flop (Toggle Flip-Flop)
Function: Works as a binary toggle switch, changing states on every clock pulse.
• Derived From: JK Flip-Flop with J = K = 1.
• Truth Table:
T Clock Q (Next State)
0↑ No Change
1↑ Toggle (Q → Q')
• Feature: If T = 1, the output flips every clock pulse.
• Application: Used in counters, frequency division circuits.
3. Flip-Flop Timing Parameters
• Setup Time (Tsu): Minimum time before the clock edge that data must be stable.
• Hold Time (Th): Minimum time after the clock edge that data must remain stable.
• Propagation Delay: Time taken for the output to respond to the clock input.
• Clock-to-Q Delay: Time taken for Q to update after a clock edge.
4. Flip-Flop Applications
Flip-flops are used in:
• Registers (storage of multi-bit data)
• Counters (binary counting circuits)
• Frequency Dividers (reducing signal frequency)
• Shift Registers (serial-to-parallel conversion)
• Finite State Machines (FSMs) (used in digital system design)
5. Study Resources
Books:
1. "Digital Design" by M. Morris Mano
2. "Digital Logic and Computer Design" by M. Morris Mano
3. "Fundamentals of Digital Logic with VHDL Design" by Stephen Brown & Zvonko Vranesic
Online Courses & Tutorials:
• NPTEL (IIT Digital Electronics Lectures)
• Coursera - Digital Electronics Fundamentals
• YouTube Channels (ECE Concepts, All About Electronics, Neso Academy)
6. Summary
Flip-Flop Type Input(s) Output Behavior
SR Flip-Flop S, R Set/Reset state, but has an invalid condition
D Flip-Flop D Output follows input D on clock edge
JK Flip-Flop J, K No invalid state, toggles when J = K = 1
T Flip-Flop T Toggles output every clock pulse
